The use of catheters to probe and treat internal body sites, via systemic routes, is becoming increasingly important in medicine. Catheters are presently used in a variety of non-surgical procedures, including blood-flow and tissue imaging by angiography, cauterizing procedures involving laser fiber optics, and localized systemic drug delivery.
Potentially, the use of catheters to inject fluid material into a localized tissue region can provide a valuable tool for treating solid cancers or other localized tissue pathologies. However, catheter methods available heretofore have generally been of limited use for this purpose. With many solid tumors (or other diseased tissue regions), the target tissue is supplied by a major artery through a group of smaller branch arteries. To deliver material into the target branch arteries using conventional procedures, a catheter is positioned in the supply artery just upstream of the target arteries, and drug is then released into the bloodstream. Since fluid flow follows the least resistance, retention of material within the larger artery is favored and a large portion of the material injected into the site will be carried downstream of the tumor site and taken up by non-tumor tissue.
The portion of an injected material which flows into the branch arteries, in the above blood-supply configuration, may be increased by occluding the major artery just downstream of the target branch arteries. The artery may be occluded conveniently by an inflatable balloon carried at the distal end of a catheter tube. This approach may still be unsatisfactory, particularly for drug delivery within a relatively long arterial segment, where the concentration of injected material may be quite variable along the length of the segment.
It may be advantageous, in delivering material to a selected tissue site, to infuse the material at a flow rate which is less than normal blood flow rate. Where the injected material is a drug, the slower infusion rate can lead to increased drug extraction by prolonging the dwell time within the tissue's vascular bed. Using catheters of the type known in the prior art, it has been difficult to achieve a controlled flow rate by injection of material into an arterial segment.
Catheters have also been used for transferring material to or from veins, for example, for sampling venous blood to determine hormone or drug levels. Often it is desired to sample venous blood from a localized tissue region, that is, a region whose venous network feeds into a defined segment of a vein. With catheters of the type available heretofore, it has been difficult to obtain such sampling.